1. Field of the Invention
This application is related to computer data exchange, and more particularly to techniques for edge correlation between design objects.
2. Background Information
Modern engineers, and in particular engineers who design mechanical devices, utilize computer aided design equipment to assist in the design process. This equipment typically consists of a UNIX-based, or Microsoft Windows NT (™)-based workstation or computer that includes a keyboard, a display, and a pointing device, such as a mouse. More particularly, the equipment includes computer aided design (hereinafter “CAD”) software that allows the engineer to create two- or three-dimensional drawings of the devices the engineer designs.
Occasionally the CAD software does more than simply allow the engineer to create drawings of these devices. The CAD software might also perform various solid modeling and/or engineering manufacturing based analysis on the engineer's CAD model, as well as certain supply chain functionalities—for example by integrating the CAD model into a sophisticated product data management (“PDM”), manufacturing resource planning (“MRP”), or enterprise resource planning (“ERP”) database system.
There are two standard paradigms in which engineers enter data into a CAD system. For the sake of simplicity, one paradigm will be referred to as the “explicit geometry” paradigm and the second will be referred to as the “parametric feature-based” paradigm. FIG. 1 shows an explicit geometry system, while FIG. 2 shows a parametric feature-based system.
In legacy CAD systems, explicit geometric specification of parts is performed. For example, images are created, sometimes in different layers, where rectangular or polar coordinates are specified for each point or line. While this method is cumbersome and painstakingly detailed, it is often a preferred data entry paradigm for engineers who design complex free-form surfaces. The strength of this paradigm is also its weakness: namely, the rigid and often unforgiving interdependencies between edges, connections, voids, and spatial geometry. For instance, moving a single line or point can disrupt the entire model.
In the not too distant past, a new approach to CAD design, called parametric feature-based (“PFB”) design was introduced. Parametric feature-based design is currently the leading design paradigm in the CAD industry. In this paradigm, which has been pioneered by companies such Parametric Technology Corporation (“PTC”), rather than explicitly reciting geometric points and the like, engineers start with certain shapes and define parameters for those shapes. Subsequent features are added to the shape that, when aggregated, form a complete CAD model. Referring to FIG. 2, it shows an exemplary feature list 4 for an object and the resulting sketch 8 of the object.
For instance, if an engineer were designing a new wheel for a car, she might start with a circle. Next, a feature is added to the circle making it a cylinder (e.g. an extrude operation). A shell could then be subtracted from the cylinder, thereby creating and overall contour for the visible part of the wheel. Finally, an array of small diameter cylinders could also be subtracted from the visible part of the wheel to create openings through which the wheel can be attached to the car. With each of the features added to the design, the engineer specifies a basic geometry and one or more parameters for the geometry (for example, radius, length, width, depth, material, etc.). In a competitive system, however, more complex shapes may be modeled. For instance, rather than starting with a baseline geometric feature, the competitive CAD system may allow cylinders, cones, or other complex three-dimensional features to be specified.
The strength of parametric feature-based design is that the engineer's design intent can be maintained, even though the details (parameters) change. This is to say that the overall design is preserved while giving the engineer the flexibility to simply test different parameters on her design. For instance, small changes to a feature on a PFB CAD model will not necessarily disrupt the stability of the entire design.
As of this writing, there are a number of major vendors of CAD software, and even more smaller vendors. These vendors include: PTC, Dassault Systemes (France), Unigraphics Solutions, SDRC, and Autodesk. Each of these vendors implements their design methodologies in a different manner and most treat their computational and algorithmic methodologies as proprietary. Not only are their methodologies secret, but the data structures that implement their methodologies are secret.
And herein lies a problem. When the users of different CAD systems need to share design data they are currently able to do so only to a limited extent. Typically the extent to which the users are able to share data is limited by the amount of co-operation between the various CAD vendors. Because the CAD vendors are head-to-head competitors, they share information only reluctantly—lest their trade secrets or proprietary methodologies, which are the very core element that distinguishes vendor from vendor (apart from their user interface), become known by their competitors.
Nevertheless, the CAD vendors have implemented certain application programming interfaces (“APIs”) that provide at least a partial solution to the problem. Using an API, a user or system integrator can make function calls to a particular CAD system together with the necessary processing information. The particular CAD system will process the function calls and may return either an explicit geometric expression of the desired part or feature, or it may return some sort of standard graphical representation of the desired part or feature.
But the APIs are functionally limited and often have significant problems exchanging complex design features and/or information. And again, every additional function added to a CAD vendor's API provides a window through which the vendor's competitors can view, with an eye to reverse engineering, at least some portion of the vendor's trade secrets.
The problem is getting worse. Consolidation in certain industries, such as the automotive and aircraft industries, creates more CAD data exchange problems. For instance, Boeing Corporation recently acquired McDonnell Douglas Corporation. The formerly separate entities likely use different CAD systems. Moreover, each formerly separate entity has multiple tiers of suppliers—each supplier using their own CAD system too. When an engineer at Boeing changes a part, that change must be communicated to the particular supplier that manufactures the part. The supplier may require the CAD model for the part. But because of incompatible file types and differing computational and algorithmic methodologies, the CAD model cannot be provided. Even worse, when Boeing decides to create design synergies between the two merged entities, the Boeing engineers and the McDonnell Douglas engineers might be completely unable to exchange complex CAD models. Of course, the same is true of Ford Motor Company, which recently purchased Jaguar and Volvo. FIG. 3 diagrammatically presents the communication problem.
The economies of scale desired by the merger of such entities are victims of the inevitable battles over sharing information and know-how between the CAD vendors. Moreover, the collaboration between engineers from separate entities (i.e., between original equipment manufacturers and first and second tier suppliers), under the current state-of-the-art, will be all but impossible—as engineers waste time and money desperately trying to share design files made from disparate CAD systems. While standards may exist for exchanging raw data images (e.g., TIFF and JPEG) and boundary representations (e.g., IGES and STEP), these standards do not preserve the design intent of the engineer.